Project Summary Outcomes following solid organ transplantation (SOT) are generally excellent with 5-year survival exceeding 85% for most graft types and age groups. Immunosuppression nonadherence is an important factor leading to graft failure and patient mortality in SOT recipients since individuals are required to make a lifelong commitment to a strict medication schedule. Nonadherence has been reported to range from 15 to 40% among liver patients and more than 30% among kidney patients. Mobile applications (?apps?) provide a low-cost and scalable opportunity to improve medication adherence through more consistent monitoring, earlier detection of nonadherence, and frequent patient-provider communication with nonadherent patients. We have developed a patient-facing mHealth app, mDOT for Transplantation, that enables patients to view their immunosuppression regimen, record themselves taking doses of their medication, track and visualize progress on their own and with their transplant coordinator, document symptoms and side effects, and access educational content. There is a transplant provider web- based platform where they can review patient submitted videos, provide feedback about accepting the video as evidence of adherence, and receive notifications when patients report symptoms. The proposed project seeks to optimize this tool to increase medication adherence in transplant recipients. The aims of the project are: 1) to enhance mDOT for Transplantation with 2-way patient-provider communication/messaging capabilities and standardized text messages to promote behavior change and 2) to perform a pilot randomized controlled trial of mDOT for Transplantation compared to standard-of-care in SOT patients.